As a disk storage unit of this kind, there has been known a hard disk drive which stores data by magnetizing a magnetic material evaporated on a disk by using a magnetic head.
In recent years, the hard disk drive has been widely used in general households owing to widespread use of personal computers in general households and owing to the advent of digital electric household appliances such as TVs, set-top boxes and TV game devices incorporating the hard disk drive.
An important function required by the hard disk drive under the above circumstances may be noise reduction.
The operational noise of the hard disk drive can be reduced by:    (1) a method of suppressing the propagation of a generated noise by wrapping the hard disk drive with a sound-absorbing material;    (2) a method of reducing the noise itself generated by the hard disk drive by reducing the diameter of the disk, reducing the rotational speed of the disk, reducing the operation speed of the head, or improving the bearings; and    (3) a method of canceling the noise by using an active noise canceller which generates a sound with a phase opposite to that of the operational noise of the hard disk drive.
According to the above method (1), however, a problem arises that is concerned with how to radiate heat generated by the hard disk drive and, hence, cost and size of a hard disk drive housing.
According to the above method (2), it becomes necessary to newly develop a hard disk drive or parts thereof for reducing noise which would cause problems such as increased cost of development, drop in a data transfer rate, and increase in a unit bit cost. When the disk rotational speed and the head operation rate are lowered, in particular, it becomes very difficult to reduce the noise while maintaining the performance.
According to the method (3), the active noise canceller must have an improved response performance in the signal processing and, hence, cannot be cheaply realized.